STUDIES IN FRAMING EFFECTS OF WAFFLE SLAB FLOOR SYSTEMS

Abstract

Waffle-slab has had its genesis in a rather thick solid-slab floor from which the bottom layer concrete in tension is partially replaced by their ribs along orthogonal directions. The concrete replacement and rib formation is done through appropriate size waffle formwork. The ribs are reinforced with steel to resist flexural tensile stresses. At this stage, the dimensions and spacing of ribs become a matter of choice to be decided in a manner so as to achieve better load distribution (structural efficiency). The spacing of the ribs are so kept as to obviate the need for shear reinforcement as also to make the system structurally behave as a slab rather than a system of interconnected parallel beams (Grid floor). Waffle-slab may be rested on a system of vertical supports (walls) in which case the floor moment and deflection get concentrated near the mid-span. The floor, on the other hand, can be framed into the vertical structural system such that there is dispersal of floor moment and deflection. There is lateral shifting of moment and deflection from the mid-span zone towards the supports. Thus, floor framing with the help of wide Band beams rigidly connected to a system of columns becomes an obvious choice. The structural efficiency of waffle slab is function of depth of slab , spacing of ribs and torsional resistance capacity of Band beam. When torsional resisting capacity of band beams are increased results in controlling the deflection of waffle slab. These studies have been carried out _aay-stady. Analyses have been carried out by stiffness matrix method. Feasibility of structural design of member have been ensured under provision of IS 456:2000. Results have been presented in suitable tabular fashion so as to arrive at appropriate conclusions.